The present invention refers to a system for damping noise produced by railroad wheels during the travel by railroad vehicles and particularly to a damping ring in the wheel.
Known devices intended for the reducing the noise produced by railroad wheels may be grouped under the following types:
Resilient wheels: on such wheels, the rim of the wheel is constituted by a bandage joined to the rest of the wheel by means of elastic elements. PA1 Damped wheels: wheels on which dampers are added by means of external elements: a) by viscoelastic elements, such as foils and rubber elements, adhered to the wheel and tuned for different frequencies, and b) by friction, such as elements joined to the wheel, which cause relative slippage as regards the surface of the wheel, producing friction which provides damping. PA1 arrangement of the ring, which is tied down in a housing preformed on the end of the wheel rim; PA1 comprises a torque system or controlled contact between the ring and the rim, which may be achieved by means of through-screws passing through the rim, or by means of a fit; PA1 shape of the ring, with a cross section of straight sides, having for example, a trapezial or rectangular section, optimizing the mass of the ring; PA1 preferably a whole ring, of one piece, although it may be divided into two or more parts by means of transverse cuts to facilitate its assembly; PA1 ring assembly on the inner side of the rim, on the outer side or on both sides simultaneously.
The object of the invention is found in this latter subgroup.
In noise damping by friction, the use of a circular sectioned ring is known, tied down in a groove or channel with semicircular section on the inner part of the wheel rim. However, in this arrangement, there are no elements which permit control over the uniformity of contact and the circumferential torque. Besides, the assembly process induces differences in the contact between different points. On the other hand, the arrangement provides little mass for a specific width of the groove or channel, movement of rigid solids may be produced, and it is impossible to displace the channel up to the flat external surface of the rim.
The inventors have confirmed that there are three main parameters for the efficacy of noise damping systems by friction: a) ring mass; b) optimization of the contact area between ring and wheel; and c) position of the ring with respect to the wheel rim.
Upon increase of the ring mass (the mass-ring/mass-wheel relation increases) an increase in the damping of the system is produced, and its efficacy improves (both in average and in high frequency). It is therefore beneficial to increase the mass of the ring as much as possible.
For a specific width in the groove or channel where the ring is housed, it is advisable that the shape of the ring offer the greatest possible mass.
Regarding the second parameter, it has been confirmed that the contact area between the surfaces of the ring and of the wheel constitutes another main parameter of the system, because the noise damping mechanism is ultimately based on the friction produced in the contact between the two surfaces by microslippage between them.
The slipping work depends on: EQU (W=.mu..N.I.):
where .mu. is the friction coefficient, N the normal load between the surfaces and I the relative slippage between both surfaces.
Given a coefficient .mu., upon increase of the normal load between the surface, the work of the friction may increase (N increases) though however, the possibility of movement is made more difficult (could decrease I). Consequently, a compromise solution exists in which, for a specific torque between the surfaces, an optimum exists in the work of the friction.
On the other hand, besides achieving a specific torque, it is important to achieve uniformity in the contact area between ring and wheel. Non-uniform contact produces the existence of zones which work adequately and zones which do not work (even with lack of contact); including the possibility of movement of the rigid solid of the ring as regards the wheel, according to which, the system would work in a totally different manner. All this causes a decrease in the global efficacy and possible dispersions of the results.
Finally, regarding the third parameter, the position of the ring with respect to the wheel rim, the research carried out shows that between the different positions of a possible damping ring, within the width of the wheel rim, the end positions (removed from the midplane, perpendicular to the wheel axis) are more efficient and, particularly, the inner side of the wheel (side of the flange) is slightly more favorable.